Analysis of ratio of embedded depth of multi-pivot secant piles to excavation depth in Suzhou subway stations

Taking a foundation pit of Nanshijie station in Suzhou subway as an example, the relationship between the ratio of the embedded depth of the secant pile to the excavation depth and the deformation of the foundation pit and the internal forces of the retaining structure is analyzed to determine the suitable embedded depth by deep excavation design software. The results show that the maximum lateral displacement of the secant pile wall does not reduce monotonously with the increase in the ratio of the embedded depth to the excavation depth, and it is little affected by the increase in the ratio of the embedded depth to the excavation depth when the ratio reaches a certain value. The similar regularity can be found in the influence of the ratio of the embedded depth to the excavation depth on the maximum ground surface settlement, the maximum axial force of each support, the maximum bending moment and shear force of the secant pile wall. Therefore, it is considered to be optimum when the ratio of the embedded depth of the secant pile to the excavation depth in Suzhou subway stations is between 0.7 and 0.8 after checking computations of stability of resistance to penetrability. This reference range can not only guarantee the stability of the foundation pits and the security of the retaining structures, but also reduce the engineering quantity and the construction costs. And the suggested values still have large safety reserve. This study provides a reference for the design of the foundation pits of other subway lines and urban high-rise buildings.